Add support for notifications to “LaTeX Watch”

We now show a notification window instead of a dialog window if there
is an error in a document. This is currently considered a work in
progress for the following reasons:

- After there is one error the window will only be updated if there are
  still errors in the document. If there are no more errors the window
  will just display the errors the document contained right before they
  were fixed.

- If we close the notification window it will never show up until we
  invoke “Watch document” again.
Close notification when typesetting succeeds

We now close an opened notification window in “LaTeX Watch” if the
document does not contain errors anymore.
Remove unused code from `texparser`

 #ignore
Add additional information to notification window

We now also display the location and severity (Error, Warning) of
errors messages in the notification window of LaTeX Watch.
Handle manual closing of notification window

Before this change manually closing the window would mean that it would
never reappear again. We would need to stop watching the document and
then invoke “Watch document” again to get the notification window back.
Left justify severity in notification window
Handle log messages containing double quotes

Before this change showing messages containing double quotes in the
notification window would fail.
Properly close file in `guess_tex_engine`

#ignore
Remove unnecessary function call in “LaTeX Watch”

#ignore
Only parse log file if there were changes

Before this change error markers and the notification window could
disappear even though the file still contained errors. This would
happen if we saved the document without making any significant changes.
In this case `latexmk` would essentially generate a log which would
report that there were no changes at all. We would parse this log and
find no error messages. This would leave `texparser` with the
impression that there were no errors. It would therefore remove old
gutter marks. `latex_watch` would close the notification window since
`latexmk` reported no errors (exit status 0).
Improve readability of verbose log output
Improve rewrap code in `texparser`
Improve reopening of closed notification windows

We now also reopen a closed notification window when the state of the
document has not changed. Before this commit a closed notification
window would not reappear if we just saved the file without making any
significant changes to the document.
Close notification window on cleanup
Do not store duplicate error messages anymore

Before this change it would be possible that the same error message
would show up multiple times in the notification window.
Sort error messages by line number

Error messages in the notification window will now be sorted according
to their line number.
Display default message in notification window

If `texparser` could not find any error messages containing line
information, then it will now show a generic default error message in
the notification window.
Remove unused code from `latex_watch`

#ignore
Extend list of auxiliary files

We now also remove `.nav` and `.snm` files. These files are usually
generated when we typeset a “beamer” presentation.
Fix missing logname in default error message